For example, such positioning devices are used to position electronic components on a printed circuit board, or perhaps to machine flat workpieces using a tool.
European Patent No. 2 066 996 describes a positioning device in a gantry-type construction in which, supported movably between two parallel linear guides is a cross bar on which a functional element is movably supported with the aid of a further linear guide, so that this functional element is able to be positioned freely in one plane between the two parallel linear guides. For example, a gripper of an automatic pick-and-place machine, a laser of a laser machining center, or a probe system of a coordinate measuring machine are possible as functional element.
European Patent No. 2 066 996 deals primarily with the most precise position measurement possible in connection with such positioning devices, since precise positioning of the functional element is often very important.
German Published Patent Application No. 10 2009 008 900 also deals with such positioning devices in gantry-type constructions. For various reasons, they are not easy to control from the standpoint of automatic control engineering. Therefore, a device is described for controlling a positioning device automatically, which permits particularly precise positioning.
However, if the functional element, which is guided on the cross bar and positioned above the workpiece, must exert considerable force on the workpiece, this may lead to deformation of the components of the positioning device. Because of the great leverage which results due to the gantry-type construction, small deformations may lead to a considerable displacement of the point of application of the tool on the workpiece, which is unacceptable for practical applications with a high requirement for positioning accuracy. An example for such an application is thermocompression bonding, in which electronic components are joined to a printed circuit board by pressure and temperature. Forces up to 500 N are necessary for this purpose. On the other hand, positioning accuracy in the range of one micrometer and less required in such and comparable applications is not uncommon.